The embryonic gut tube is composed of an inner layer of endoderm and an outer layer of mesoderm. Molecular interactions between these two layers over the course of development result in the regional patterning of the gut into esophagus, stomach, small intestine and large intestine; each region adopts a distinct epithelial morphology and gene expression profile. Occasionally, in lesions known as intestinal metaplasia, epithelium with the characteristics of small intestine, are observed in regions of the stomach and esophagus. Clinically, such lesions are associated with the later development of adenocarcinoma. Neither the molecular cascades that control regional patterning of the gut during ontogeny nor the genetic alterations that result in intestinal metaplasia are well understood. To begin to examine these processes at a molecular level, the transcriptional regulation of a small intestinal marker gene will be studied. This gene, villin, is transcriptionally activated upon gut tube formation, and is upregulated during morphogenesis of small intestinal villi. At 16 days of mouse development, the villin gene suddenly adopts a one-cell thick expression border in the pyloric endoderm, marking the differentiation of stomach vs. intestinal compartments. Villin is also consistently expressed at high levels in intestinal metaplasias. Thus, the factors that regulate villin expression are likely to be (at least some of) the same factors that are important for intestinal organogenesis and for generation of intestinal metaplasias. The following hypotheses are tested: 1) The molecular factors underlying patterning of the intestine can be deciphered by analysis of the cis and trans factors that regulate a marker gene whose expression correlates with events of intestinal differentiation (villin). 2) Villin responds to an important event in epithelial patterning that occurs at 16 days and may involve cell identity decisions (stomach vs. intestine). 3) Some of the same factors that specify the intestinal phenotype during ontogeny are also responsible for the generation of the intestinal phenotype in intestinal metaplasia. Aim 1 uses transgenic mice, cell culture and DNA binding studies to examine the cis and trans factors that regulate villin expression during ontogeny. In Aim 2, differential display analysis is used to identify transcripts associated with the development of the distinct epithelial pyloric border in the developing mouse embryo. In Aim 3, transgenic mice carrying wild type and mutant villin regulatory fragments (linked to beta-galactosidase) are tested in mouse models of intestinal metaplasia developed by other Program Project members to identify the cis elements that are important for villin up-regulation in intestinal metaplasias. These studies are likely to reveal factors that control gut ontogeny, epithelial patterning, and/or epithelial cell identity decisions relevant to gut organogenesis and to the development of intestinal metaplasias.